fix(electron): inline TS helpers so the sandboxed preload keeps working

The frame pump's async/await (target es2015 + importHelpers) made webpack
externalize tslib in main.preload.js. Sandboxed preloads can only require
Electron's built-in module whitelist, so the entire preload script failed
to load and window.electron disappeared for every run without the
frame-copy flag. importHelpers:false for electron-backend keeps the preload
bundle self-contained — and future async code in preload can no longer
silently reintroduce the breakage. Verified live: sandboxed run now has the
bridge, reports engine 'native' and frameCopyAvailable true.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

apps/electron-backend/tsconfig.app.json

@@ -2,7 +2,8 @@
     "extends": "./tsconfig.json",
     "compilerOptions": {
         "outDir": "../../dist/out-tsc",
-        "types": ["node"]
+        "types": ["node"],
+        "importHelpers": false
     },
     "files": ["../../global.d.ts"],
     "exclude": [